Well, I've rebuilt over 15 car engines in my life, both top and bottom ends. Two stroke dirtbike engines, Four stroke dirtbike engines, and a few streetbike engines. MedRX is no better than the Chevron Techron, the Lucas Oil fuel additives, and most of the 10 other top shelf fuel additives. They all contain the same active ingredient, PEA and anyone who says that their "other" ingredients are superior are basically doing the old snake oil sales techniques. Ill explain below.
Yamalube does not manufacture MedRX or Ringfree. Like Honda, they purchase and repackage/white label their oils and additives from petroleum/chemical firms. The active ingredient in most fuel additives that do the "cleaning" per say is Polyether-amine, or P.E.A. as it is better known. It's a nitrogen based detergent that cleans the top end of engines and fuel injectors and deals with the total crap that is in our gas here in the USA now days. Including Ethanol.
There are only like 8 companies who actually manufacture fuel additives and oils, and then companies like gumout, royal purple, redline, Honda, Yamaha, Napa etc, etc purchase in bulk and package them under their names. Most all are about the same, with PEA Nitrogen as the active ingredient and some with other additives added in for marketing or fuel stabilization.
Chevron even patented "Techron" for marketing purposes, but it too is just PEA with their stabilizer added. This allows them to market the superior technology and all that bull.
PEA is what is used in all fuel additives, sometimes they call it something different but its basically a strong nitrogen formula. It is the strongest detergent additive available, this is why all fuel additives use it as the main ingredient.
Any top shelf fuel additive with PEA in it works fine. I premix my dirt, street and snowmobile fuels with non ethanol 93 octane fuel and Royal Purple 10722 additive in five gallon race jugs. I use top end oil for the two strokes.
I like the Royal purple because it has a strong fuel stabilizer so it can sit over the winter and the fuel won't go bad. But really , to determine the best addiive, dont worry so much about the brand, and just read the labels and pick the one that has the highest % of PEA for the lowest cost. EVerything else is just BS marketing.
It also costs a whole hell of a lot less than anything sold at a USA bike dealership. A lot of the guys I race hare scrambles with use it as well, including the service manager at my local Yamaha Dealership. 😉